WO2015087911A1

WO2015087911A1 - Light modulation device and display device

Info

Publication number: WO2015087911A1
Application number: PCT/JP2014/082674
Authority: WO
Inventors: 佐々木　貴啓; 弘幸森脇; 花岡　一孝
Original assignee: シャープ株式会社
Priority date: 2013-12-13
Filing date: 2014-12-10
Publication date: 2015-06-18

Abstract

The present invention provides a light modulation device whereby it is possible to enhance control of light transmissibility when imparting a voltage by efficaciously controlling the alignment of shape anisotropic particles, and a display device which is provided with the same. The present invention is a light modulation device provided with: a first substrate and a second substrate which are positioned in mutual opposition; and a light modulation layer which is positioned between the first substrate and the second substrate. The first substrate is provided with a pair of electrodes. The light modulation layer has shape anisotropic particles dispersed in liquid crystals. The liquid crystals and the shape anisotropic particles are aligned perpendicularly with respect to the first substrate when a voltage is not imparted between the pair of electrodes, and are inclined horizontally with respect to the first substrate in a lateral electrical field wherein the voltage is imparted between the pair of electrodes. A polymer layer which has a surface shape which assists the inclination of the shape anisotropic particles in the lateral electrical field is disposed upon the surface of the first substrate toward the light modulation layer side.

Description

Light modulation device and display device

The present invention relates to a light modulation device and a display device. More specifically, the present invention relates to a light modulation device and a display device that perform light modulation by controlling the direction of shape anisotropic particles dispersed in liquid crystal.

As a light modulation device, a liquid crystal panel using a polarizing plate is well known. In this method, natural light before entering the liquid crystal layer is converted into polarized light by the polarizing plate, and the polarized light transmitted through the liquid crystal layer is converted into the same polarizing plate (in the reflection mode) or another polarizing plate (in the transmission mode). By making the light incident, the transmittance of light incident on the liquid crystal panel can be controlled. The liquid crystal layer can be used for controlling the polarization state because the orientation of the liquid crystal molecules in the liquid crystal layer changes depending on the magnitude of the applied voltage. This type of liquid crystal panel has a limit in improving the light utilization efficiency because more than half of the light used for display is absorbed by the polarizing plate.

Therefore, development of a light modulation device that does not require a polarizing plate is underway. For example, those disclosed in Patent Documents 1 to 8 are known.

Patent Document 1 discloses an optical device in which a system including electro-optical sensitive flakes suspended in a liquid host is encapsulated in a polymer binder solution. Patent Document 2 discloses a display medium in which scaly magnetic powder is dispersed in a liquid in a microcapsule surrounded by a binder. Patent Document 3 discloses an electrochemical display element in which an ionic conductor composed of fine particles of a specific type of organic polymer and an electrolytic solution held in the fine particles of the polymer is sandwiched between two electrode plates. It is disclosed.

Patent Documents 4 and 5 disclose a light modulation panel including a light modulation layer including a shape anisotropic member. Patent Documents 6 and 7 disclose an optical device including a suspension layer containing polymer flakes. Patent Document 8 discloses a transflective display having a suspension layer containing reflective particles.

Furthermore, in the field of the liquid crystal panel using the polarizing plate described above, a polymer supported alignment (PSA) technique has been known as a technique capable of improving response speed and aperture ratio (for example, And Patent Documents 9 to 11). Patent Document 9 discloses a PSA technique in which a monomer (monomer) is dispersed in a liquid crystal, and the monomer dispersed in the liquid crystal is photopolymerized by irradiating light while applying a voltage to the liquid crystal. It is described that a polymer (polymer) is formed on the surface, and the initial tilt (pretilt) of the liquid crystal on the alignment film surface is fixed by this polymer.

Special table 2003-533736 gazette JP-A-6-313880 JP 2006-235484 A International Publication No. 2013/108899 International Publication No. 2013/141248 US Pat. No. 6,665,042 US Pat. No. 6,829,075 Special table 2007-506152 International Publication No. 2008/18213 JP 2002-357830 A JP 2003-307720 A

As a result of various studies on a light modulation device that does not require a polarizing plate and is suitable for improving the light utilization efficiency, the present inventors have focused on a display method in which shape anisotropic particles are operated by voltage application. However, the conventional light modulation device using this display method has room for improvement because a desired light transmittance cannot be obtained when a voltage is applied. For example, when applied to a display device that displays white by reflecting light with shape anisotropic particles when a voltage is applied, it has been required to make the white display brighter.

The present invention has been made in view of the above situation, and a light modulation device capable of improving the control of light transmittance at the time of voltage application by effectively controlling the orientation of shape anisotropic particles, and the same An object of the present invention is to provide a display device including

The present inventors have found that if liquid crystal is used as a medium for dispersing shape anisotropic particles, the orientation of the shape anisotropic particles can be controlled by utilizing the change in the alignment state of the liquid crystal due to voltage application. . However, as a result of further investigation, there is still room for improvement in the orientation control of the shape anisotropic particles even if the change in the alignment state of the liquid crystal due to voltage application is used in addition to the dielectrophoresis of the shape anisotropic particles. I understood. Therefore, the present inventors paid attention to the PSA technique as a means for effectively controlling the orientation of shape anisotropic particles. By applying the PSA technology, shape anisotropic particles that are not oriented in the desired direction are reduced in a state where a voltage is applied to the light modulation layer, and the control of light transmittance during voltage application can be improved. Actually found. As described above, the present inventors have conceived that the above problems can be solved brilliantly, and have reached the present invention.

That is, an aspect of the present invention is a light modulation device including a first substrate and a second substrate that are disposed to face each other, and a light modulation layer that is disposed between the first substrate and the second substrate. The first substrate has a pair of electrodes, the light modulation layer is a liquid crystal in which shape anisotropic particles are dispersed, and the liquid crystal and the shape anisotropic particles are in the pair. In a state where no voltage is applied between the electrodes, the substrate is oriented in a direction perpendicular to the first substrate, and a voltage is applied between the pair of electrodes. A light modulation device in which a polymer layer having a surface shape that supports the inclination of the shape anisotropic particles in the transverse electric field state is provided on the surface of the first substrate on the light modulation layer side It may be.

Another embodiment of the present invention may be a display device including the light modulation device.

According to the light modulation device of the present invention, when the light modulation device is driven, the shape anisotropic particles are provided by providing the polymer layer having a surface shape that supports the inclination of the shape anisotropic particles in the transverse electric field state. Can be easily oriented in a desired direction according to the transverse electric field, and the control of the light transmittance during voltage application can be improved (expansion of dynamic range). That is, if it is a usage mode that transmits light when a voltage is applied, the light transmittance at the time of voltage application can be further increased, and if it is a usage mode that blocks light when a voltage is applied, the light transmittance at the time of voltage application Can be made lower. Furthermore, the response speed with respect to the applied voltage of the shape anisotropic particle at the time of driving of the light modulation device can be improved.

In addition, since the display device of the present invention includes the light modulation device as described above, it has excellent light utilization efficiency that does not require a polarizing plate, and the display performance when a voltage is applied is improved. When applied to a reflective display device that performs display using reflection of external light, white display when a voltage is applied can be brightened. On the other hand, when applied to a transmissive display device that transmits light from a light source and performs display, black display when a voltage is applied can be made darker. Furthermore, the response speed of the pixels when driving the display device can be improved.

It is a cross-sectional schematic diagram of the light modulation device of the first embodiment, (a) represents the voltage off state, (b) represents the voltage on state. 3 is a schematic plan view illustrating an electrode structure of a lower substrate in the light modulation device of Embodiment 1. FIG. It is a cross-sectional schematic diagram of the light modulation device according to the first embodiment before and after the formation of the PSA film, where (a) represents a state before the PSA process, and (b) represents a state during the PSA process. It is a cross-sectional schematic diagram of the light modulation device of Embodiment 2, (a) represents a voltage off state, (b) represents a voltage on state. 6 is a schematic perspective view illustrating an electrode structure in a light modulation device according to Embodiment 3. FIG. It is the photograph which compared and showed the white display state of the area | region (right side of a figure) to which the PSA process was performed, and the area | region (left side of the figure) where the PSA process was not performed. It is the microscope observation photograph which expanded and showed the area | region where the PSA process shown in FIG. 6 was not performed. It is the microscope observation photograph which expanded and showed the area | region where the PSA process shown in FIG. 6 was performed. 5 is a graph showing reflectance-voltage characteristics (RV characteristics) of a PSA untreated area and a PSA treated area.

Hereinafter, embodiments and examples of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments and examples. Although the use of the light modulation device in the following embodiments is a display device (flake display), the use of the light modulation device of the present invention is not limited to the display device, and for example, adjustment of show window, blind, and white turbidity is possible. Application to frosted glass is also possible. In addition, the configurations of the embodiments and examples may be appropriately combined or changed without departing from the gist of the present invention. In addition, in each embodiment, the same code | symbol is attached | subjected to the member which exhibits the same function.

[Embodiment 1]
The light modulation device of Embodiment 1 constitutes a reflective display device that performs display using reflection of light (external light) incident from outside the device into the device, and performs black display when no voltage is applied. When a voltage is applied, white display or halftone display (gray display) is performed. The light modulation device according to the first embodiment includes a plurality of pixels arranged in a matrix, and is configured to be able to switch between black display, halftone display, and white display in each of the plurality of pixels. .

An outline of the configuration of the light modulation device according to the first embodiment will be described with reference to FIGS. 1 and 2. 1A and 1B are schematic cross-sectional views of the light modulation device according to the first embodiment. FIG. 1A illustrates a voltage off state, and FIG. 1B illustrates a voltage on state. FIG. 2 is a schematic plan view showing the electrode structure of the lower substrate in the light modulation device of the first embodiment.

The light modulation device according to the first embodiment includes a liquid crystal layer 30 as a light modulation layer between a first substrate 10 and a second substrate 20 that are arranged to face each other. The first substrate 10 is located on the back side, and the second substrate 20 is located on the front side (display surface side, observer side). The first substrate 10 and the second substrate 20 are bonded to each other by a sealing material (not shown) arranged so as to surround the display area. A liquid crystal layer 30 is sealed in a gap between the first substrate 10 and the second substrate 20 surrounded by the sealing material. The thickness of the liquid crystal layer 30 is not particularly limited.

The first substrate 10 includes a pair of

electrodes

12a and 12b, a vertical alignment film 14 and a PSA film 15 in this order on the liquid crystal layer side (display surface side) of the lower substrate 11, and a light absorber on the back side of the lower substrate 11. (Light absorption layer) 16 is provided. Note that the first substrate 10 is an active matrix substrate and includes switching elements arranged in each pixel and various wirings, but is not shown in the figure. As the switching element, for example, a thin film transistor (TFT) is used. Examples of the various wirings include a gate bus line that supplies a scanning signal to the TFT, a source bus line that supplies a display signal to the TFT, and a common wiring. The pair of

electrodes

12a and 12b is provided for each pixel, one of which is electrically connected to the source bus line via the switching element, and the other is electrically connected to the common wiring.

The pair of

electrodes

12a and 12b has an in-plane switching (IPS) type electrode structure, and specifically, is a pair of comb-teeth electrodes in which mutual comb teeth are fitted. As shown in FIG. 2, each of the pair of

electrodes

12a and 12b has a trunk part and a plurality of parallel branch parts (comb teeth) extending from the trunk part. They are arranged alternately with an interval (space). By applying a voltage between the pair of

electrodes

12a and 12b by the AC power supply, an electric field (lateral electric field) horizontal to the first substrate 10 is generated in the liquid crystal layer 30 near the space.

The pair of

electrodes

12a and 12b are formed of a conductive material, and can be formed of, for example, a metal material. In this embodiment, since the display is performed using reflection of external light, the electrodes in the first substrate 10 on the back side of the liquid crystal layer 30 do not have to be formed of a transparent conductive material.

The vertical alignment film 14 is disposed so as to cover at least the entire display region. That is, the initial alignment of the liquid crystal molecules 31 is set in a direction perpendicular to the first substrate 10. The vertical alignment film 14 only needs to align the liquid crystal molecules 31 in the liquid crystal layer 30 substantially perpendicularly to the surface thereof.

The PSA film 15 is a layer made of a polymer, and is provided on the outermost surface of the first substrate 10 on the liquid crystal layer 30 side. In the PSA film 15, the shape anisotropic particles 32 dispersed in the liquid crystal layer 30 are horizontally aligned with respect to the first substrate 10 by a lateral electric field generated when a voltage is applied between the pair of

electrodes

12 a and 12 b. Supports tilting. The surface of the PSA film 15 has a shape that can support the inclination of the shape anisotropic particles 32. A method for forming such a PSA film 15 will be described in detail later.

The light absorber 16 is for absorbing external light transmitted through the liquid crystal layer 30 and realizing black display. The material of the light absorber 16 is not particularly limited as long as it can absorb light. For example, a resin in which a black pigment is dispersed can be used. As described above, the light modulation device according to the present embodiment constitutes a reflective display device. When no voltage is applied, the light absorber 16 absorbs the external light transmitted through the liquid crystal layer 30 so that the black light is absorbed. Display is realized, and when a voltage is applied, the shape anisotropic particles 32 inclined in the horizontal direction due to a horizontal electric field reflect external light, thereby realizing white display or halftone display. As shown in FIG. 1, the light absorber 16 is provided on the back side of the lower substrate 11, but may be provided on the front side of the lower substrate 11.

The second substrate 20 includes a counter electrode 22, an insulating film 23, a vertical alignment film 24, and a PSA film 25 in this order on the liquid crystal layer side (back side) of the upper substrate 21. In the case of performing color display, a color filter is further provided.

The counter electrode 22 is disposed to face the pair of

electrodes

12a and 12b, but may not be disposed for each pixel. In the present embodiment, the counter electrode 22 is provided in a planar shape so as to cover the entire display region composed of a large number of pixels. By providing the counter electrode 22, a vertical electric field can be applied to the liquid crystal layer 30. The light modulation device of this embodiment basically performs display only with a lateral electric field. However, a drive incorporating a vertical electric field can be performed as necessary for resetting hysteresis, resetting flake orientation disturbance due to impact from the outside, and further assisting electric field for high-speed response.

The counter electrode 22 is preferably formed of a transparent conductive material. Examples of the transparent conductive material include indium tin oxide (ITO) and indium zinc oxide (IZO).

By providing the insulating film 23 together with the counter electrode 22, a lateral electric field can be effectively formed in the liquid crystal layer 30 during white display. Thereby, bright white display can be realized.

The vertical alignment film 24 and the PSA film 25 on the second substrate 20 side are provided in the same manner as the vertical alignment film 14 and the PSA film 15 on the first substrate 10 side.

The liquid crystal layer 30 is obtained by dispersing shape anisotropic particles 32 in liquid crystal. By using a liquid crystal as a dispersion medium for the shape anisotropic particles 32, the shape anisotropic particles 32 can be uniformly dispersed. The liquid crystal molecules 31 and the shape anisotropic particles 32 constituting the liquid crystal change their directions in the liquid crystal layer 30 in accordance with a lateral electric field applied by the pair of

electrodes

12 a and 12 b of the first substrate 10. In the present embodiment, liquid crystal molecules having positive dielectric anisotropy (Δε) are used as the liquid crystal molecules 31 in order to incline the shape anisotropic particles 32 in the horizontal direction by a lateral electric field.

The shape anisotropic particles 32 only have to have anisotropy in shape, but the projected area on the first substrate 10 in the horizontal direction from the projected area on the first substrate 10 in the vertical direction. It is preferable that the projected area continuously changes according to the inclination. As a specific example of such a shape, a flake shape such as a disk shape is preferably used. Moreover, it is preferable that the projected area on the first substrate 10 when set in the horizontal direction is twice or more than the projected area on the first substrate 10 when set in the vertical direction. The thickness of the shape anisotropic particle 32 is not particularly limited. However, the smaller the thickness, the smaller the projected area onto the first substrate 10 in the vertical direction, which is preferable. 500 nm or less). Furthermore, it is preferable that the shape anisotropic particle 32 has a light reflective surface.

Further, as the material of the shape anisotropic particle 32, a metal, a semiconductor, a dielectric, and a composite material thereof can be used. When a metal is used as the material of the shape anisotropic particle 32, it is preferable to form a dielectric layer (insulating layer) on the surface of the shape anisotropic particle 32. Thereby, since the difference in dielectric constant between the shape anisotropic particles 32 and the liquid crystal can be increased, the orientation of the shape anisotropic particles 32 can be controlled using the dielectrophoretic force. For example, a metal flake coated with a resin is preferably used. The film thickness of the resin is, for example, about several tens to 100 nm.

The specific gravity of the shape anisotropic particles 32 is preferably about the same as that of the liquid crystal from the viewpoint of preventing the liquid crystal layer 30 from floating and settling.

FIG. 1A shows a state in which no voltage is applied between the pair of

electrodes

12a and 12b. In this state, the liquid crystal molecules 31 and the shape anisotropic particles 32 are formed on the first substrate 10. It is oriented vertically. For this reason, incident external light from the second substrate 20 side passes through the liquid crystal layer 30 and reaches the light absorber 16, thereby realizing black display. In FIG. 1A, the path of external light is indicated by arrows.

FIG. 1B shows a state in which a voltage is applied between the pair of

electrodes

12a and 12b. In this state, the liquid crystal molecules 31 have a positive dielectric anisotropy. Horizontal alignment is performed with respect to the first substrate 10 according to the strength of the lateral electric field. Further, the shape anisotropic particles 32 are tilted in the horizontal direction with respect to the first substrate 10 under the force that the liquid crystal molecules 31 located around the shape anisotropic particles 32 change from vertical alignment to horizontal alignment. It is preferable that the shape anisotropic particles 32 are horizontally aligned not only by the orientation change of the surrounding liquid crystal molecules 31 but also by the dielectrophoretic force generated in itself. The dielectrophoretic force increases as the difference between the dielectric constants of the liquid crystal molecules 31 and the shape anisotropic particles 32 serving as a medium increases. Therefore, from the viewpoint of obtaining good switching characteristics, it is preferable that the difference in dielectric constant between the liquid crystal molecules 31 and the shape anisotropic particles 32 is large.

As the inclination of the shape anisotropic particles 32 increases with voltage application, the area when the shape anisotropic particles 32 are projected onto the first substrate 10 increases. As the projected area increases, the amount of external light reflected by the inclined shape anisotropic particles 32 increases. Therefore, halftone display is performed when the applied voltage between the pair of

electrodes

12a and 12b is relatively low, and white display is realized when the predetermined applied voltage is reached. In FIG. 1B, the path of external light is indicated by arrows.

The above description is based on the switching from the voltage-off state in FIG. 1A to the voltage-on state in FIG. 1B, but the voltage-off state in FIG. The case of switching to the state is the same except that the direction of the orientation change of the liquid crystal molecules 31 and the shape anisotropic particles 32 is reversed. That is, the orientation change of the liquid crystal molecules 31 and the shape anisotropic particles 32 is reversible by applying a voltage regardless of whether the orientation changes from vertical orientation to horizontal orientation or from horizontal orientation to vertical orientation. Therefore, the response speed when changing from black display to white display and the response speed when changing from white display to black display can be made equal.

In the present embodiment, since the

PSA films

15 and 25 are provided, the inclined shape anisotropic particles 32 can be supported on the surfaces of the first substrate 10 and the second substrate 20. The

PSA films

15 and 25 may indirectly support the shape anisotropic particles 32 by having a surface shape suitable for the liquid crystal molecules 31 in the tilted state, or the shape anisotropic particles 32 in the tilted state. The shape anisotropic particles 32 may be directly supported by having a surface shape adapted to the above.

Here, an example of a method of forming the

PSA films

15 and 25 will be described with reference to FIG. 3A and 3B are schematic cross-sectional views of the light modulation device according to the first embodiment before and after the formation of the PSA film. FIG. 3A shows a state before the PSA process, and FIG. 3B shows a state during the PSA process.

As shown in FIG. 3A, in the light modulation device before the PSA process, the liquid crystal layer 30 contains a liquid crystal composed of liquid crystal molecules 31, shape anisotropic particles 32, and a PSA monomer 33. Yes. As shown in FIG. 3B, during the PSA process, a voltage is applied between the pair of

electrodes

12a and 12b on the first substrate 10 side, and the counter electrode 22 on the second substrate 20 side is 0 V (GND). And As a result, the alignment state of the liquid crystal molecules 31 changes from vertical alignment to horizontal alignment, and accordingly, the alignment state of the shape anisotropic particles 32 also changes to horizontal alignment.

In the state where the liquid crystal molecules 31 and the shape anisotropic particles 32 are horizontally aligned as described above, ultraviolet rays (UV) are irradiated from the second substrate 20 side to polymerize the PSA monomer 33. As a result,

PSA films

15 and 25 are formed on the surfaces of the

vertical alignment films

14 and 24. The

PSA films

15 and 25 obtained in this manner impart a pretilt for determining the orientation direction to the liquid crystal molecules 31, so that the liquid crystal molecules 31 are more easily tilted when a voltage is applied than when the

PSA films

15 and 25 are not provided. When the liquid crystal molecules 31 are easily tilted, the shape anisotropic particles 32 that are tilted according to the liquid crystal alignment are also easily tilted, so that the brightness of white display can be improved. Moreover, the response speed with respect to the applied voltage of the shape anisotropic particle 32 can be improved.

As the PSA monomer 33, a monomer having a liquid crystal skeleton is preferable. For example, a monomer represented by the following general formula (1) can be used.
P ¹ -A ^1- (Z ¹ -A ² ) _n -P ² (1)
In the general formula (1), P ¹ and P ² are each independently an acrylate, methacrylate, vinyl, vinyloxy or epoxy group, and A ¹ and A ² are each independently 1,4-phenylene or naphthalene. A -2,6-diyl group, Z ¹ is a —COO— or —OCO— group or a single bond, and n is 0, 1 or 2.

Examples of the monomer represented by the general formula (1) include monomers represented by the following formulas (2) to (4).

P ¹ and P ² in the above formulas (2) to (4) are each independently an acrylate, methacrylate, vinyl, vinyloxy or epoxy group.

Examples of the monomer represented by the general formula (2) include a monomer represented by the following formula (5).

In the PSA process, in order to horizontally align the liquid crystal molecules 31 and the shape anisotropic particles 32, (1) pressurization and (2) heating to a temperature higher than the NI point may be performed.

(1) The thickness of the liquid crystal layer 30 from the first substrate 10 side and / or the second substrate 20 side at the time of ultraviolet irradiation in order to allow the PSA treatment to proceed with the pressure-shaped anisotropic particles 32 tilted sufficiently. The light modulation device may be pressurized so that the light intensity temporarily decreases. As a method of pressurization, surface pressing that uniformly pressurizes a predetermined surface is preferable. In-plane variation may occur in the tilting direction of the shape anisotropic particles 32 by one surface pressing, but if the voltage application and the surface pressing are used in combination, the shape anisotropic particles 32 that have fallen once become the next surface. Since the pressing hardly returns to the original vertical alignment, if the surface pressing is repeated several times while changing the position, the shape anisotropic particles 32 on the entire surface in the plane fall down, and the in-plane variation is eliminated.

(2) Heating to a temperature not lower than the NI point The liquid crystal layer 30 is once heated to a temperature not lower than the NI point, the shape anisotropic particles 32 are tilted, and thereafter the temperature is not higher than the NI point, so that the shape anisotropic particles 32 Ultraviolet irradiation may be performed while the is tilted. The NI point is a temperature at which the liquid crystal changes from a nematic phase to an isotropic liquid phase. In the liquid crystal layer 30 in which the shape anisotropic particles 32 are added to the liquid crystal solvent, when the temperature is higher than the NI point, a phenomenon is observed in which the shape anisotropic particles 32 change state from vertical alignment to horizontal alignment. . That is, when the orientation of the liquid crystal molecules 31 is changed from vertical to random by setting the temperature to be higher than or equal to the NI point, a phenomenon occurs in which the shape anisotropic particles 32 whose vertical orientation is not regulated are horizontally oriented. If this phenomenon is applied to the PSA process, the surface shapes of the

PSA films

15 and 25 can be effectively controlled.

As for voltage application, pressurization, and heating to a temperature higher than the NI point in the PSA process, any one method may be used, or two or more methods may be used in combination.

In the light modulation device of the present embodiment, the

PSA films

15 and 25 are provided so that the shape anisotropic particles 32 can be oriented in a desired direction according to the lateral electric field when the light modulation device is driven. It becomes easy and the light transmittance at the time of voltage application can be made higher. Since the reflective display device does not require a light source, it is suitable for low power consumption and thinning, while obtaining a bright white display is an important technical problem. According to the light modulation device (reflection display device) of the present embodiment, bright white display can be realized. In addition, the response speed of the pixels can be improved.

The display principle of the light modulation device according to the present embodiment is to control the reflectance of external light that is natural light by changing the direction of the shape anisotropic particles 32. Therefore, unlike the liquid crystal panel using the polarizing plate, it is not necessary to dispose the polarizing plate on the back side of the first substrate 10 and the front side of the second substrate 20. For this reason, the light modulation device of this embodiment is excellent in light utilization efficiency.

[Embodiment 2]
The light modulation device according to the second embodiment constitutes a transmissive display device that performs display using light from a light source, and performs white display when no voltage is applied and performs black display when a voltage is applied. .

4A and 4B are schematic cross-sectional views of the light modulation device according to the second embodiment. FIG. 4A illustrates a voltage off state, and FIG. 4B illustrates a voltage on state. As shown in FIG. 4, the light modulation device of Embodiment 2 includes a light source (backlight) 40 on the back side of the first substrate 10, and is emitted from the light source 40 by the liquid crystal layer 30 as a light modulation layer. The transmission and reflection of light is controlled. For this reason, the light modulation device according to the second embodiment is different from the light modulation device according to the first embodiment in that the light source 40 is included and the light absorber 16 is not included. Moreover, in this embodiment, since the light which permeate | transmitted the liquid crystal layer 30 is used for a display, it is preferable that a pair of

electrode

12a, 12b is formed with a transparent conductive material.

The method of the light source 40 may be an edge light type or a direct type. The type of the light source is not particularly limited, and a light emitting diode (LED), a cold cathode tube (CCFL), or the like can be used.

4A shows a state in which no voltage is applied between the pair of

electrodes

12a and 12b. In this state, the liquid crystal molecules 31 and the shape anisotropic particles 32 are formed on the first substrate 10. FIG. It is oriented vertically. For this reason, the light from the light source 40 incident from the first substrate 10 side is transmitted through the liquid crystal layer 30 and the second substrate 20, and white display is realized. In FIG. 4A, the path of light from the light source 40 is indicated by an arrow.

FIG. 4B shows a state in which a voltage is applied between the pair of

electrodes

12a and 12b. In this state, the liquid crystal molecules 31 and the shape anisotropic particles 32 have a transverse electric field strength. Accordingly, it tilts in the horizontal direction with respect to the first substrate 10. As the inclination of the shape anisotropic particles 32 increases, the area when the shape anisotropic particles 32 are projected onto the first substrate 10 increases. For this reason, the light from the light source 40 is reflected by the inclined shape anisotropic particles 32, and black display is realized. In FIG. 4B, the path of light from the light source 40 is indicated by an arrow.

Also in the light modulation device of this embodiment, since the

PSA films

15 and 25 are provided, the inclined shape anisotropic particles 32 can be supported on the surfaces of the first substrate 10 and the second substrate 20. Thereby, it becomes easy to orient the shape anisotropic particles 32 in a desired direction according to the transverse electric field when driving the light modulation device, and the light transmittance at the time of voltage application can be further reduced. That is, according to the light modulation device (transmission type display device) of the present embodiment, dark black display can be realized and the contrast ratio can be greatly improved. In addition, the response speed of the pixels can be improved.

The display principle of the light modulation device of this embodiment is to control the reflectance of light from a light source that is natural light by changing the direction of the shape anisotropic particles 32. Therefore, unlike the liquid crystal panel using the polarizing plate, it is not necessary to dispose the polarizing plate on the back side of the first substrate 10 and the front side of the second substrate 20. For this reason, the light modulation device of this embodiment is also excellent in light utilization efficiency.

[Embodiment 3]
The light modulation device of Embodiment 3 is the light modulation of Embodiment 1 except that the electrode structure of the first substrate is changed from an IPS electrode structure to a fringe field switching (FFS) electrode structure. It has the same configuration as the device. By adopting the FFS type electrode structure, it is possible to reduce the possibility of a short circuit between a pair of electrodes provided on the first substrate. Further, the provision of the planar electrode can prevent the influence of static electricity from the outside of the light modulation device.

FIG. 5 is a schematic perspective view illustrating an electrode structure in the light modulation device according to the third embodiment. As shown in FIG. 5, in the light modulation device of the third embodiment, the first substrate 10 is formed with the planar first electrode 112a and a plurality of parallel electrode slits (electrode non-formed portions). The second electrode 112 b is laminated via a dielectric layer (insulating film) 113. The second electrode 112b is electrically connected to the drain electrode of the TFT disposed on the lower layer (lower substrate 11 side) through a contact hole (not shown). The first electrode 112a is disposed on the entire surface of the first substrate 10 except for an opening for forming a contact hole. By applying a voltage between the first electrode 112a and the second electrode 112b, an electric field substantially horizontal to the first substrate 10 is generated in the liquid crystal layer 30 near the electrode slit. In the present specification, the “lateral electric field” includes not only a horizontal electric field formed by the IPS type electrode structure but also a substantially horizontal electric field formed by the FFS type electrode structure.

Also in the light modulation device of this embodiment, since the

PSA films

15 and 25 are provided, the inclined shape anisotropic particles 32 can be supported on the surfaces of the first substrate 10 and the second substrate 20. Thereby, the light transmittance at the time of voltage application can be made higher, and the response speed of the pixel can also be improved. Also in the light modulation device of the present embodiment, it is not necessary to dispose a polarizing plate, so that the light use efficiency is excellent.

[Modification 1 of Embodiment]
In the first to third embodiments described above, the following condition 1 is adopted, but the following condition 2 or 3 may be adopted. From the viewpoint of the followability of the shape anisotropic particle 32, the following conditions 1 and 2 are preferably used.
(Condition 1)
Liquid crystal molecules: Positive dielectric anisotropy Initial alignment: Vertical alignment Electric field direction: Transverse electric field

(Condition 2)
Liquid crystal molecules: Negative dielectric anisotropy Initial alignment: Vertical alignment Electric field direction: Vertical electric field

(Condition 3)
Liquid crystal molecules: Positive dielectric anisotropy Initial alignment: Horizontal alignment Electric field direction: Vertical electric field

[Modification 2 of the embodiment]
In Embodiments 1 to 3 described above, a combination of liquid crystal molecules having a positive dielectric anisotropy and shape anisotropic particles 32 made of a metal coated with a dielectric is used. The alignment direction of the liquid crystal with respect to the liquid crystal and the alignment direction of the shape anisotropic particles 32 with respect to the electric field can be made to coincide with each other, and the alignment control can be performed efficiently. On the other hand, when liquid crystal molecules having negative dielectric anisotropy are used (for example, the above condition 2), if a flake material made of a metal not covered with a dielectric is used, the orientation of the liquid crystal with respect to the electric field is adjusted. The direction and the orientation direction of the shape anisotropic particle 32 with respect to the electric field can be matched, and the orientation control can be performed efficiently.

[Example 1]
Based on Embodiment 1, the reflective display apparatus of the following structure was actually produced and the display characteristic was evaluated.
(1-1) Preparation of first substrate 10 An ITO (indium tin oxide) film having a thickness of 800 mm was formed on a sheet glass (lower substrate 11) having a thickness of 0.7 mm. Subsequently, the ITO film was patterned to form stripe electrodes (a pair of

electrodes

12a and 12b) having an electrode width of 4 μm and an electrode interval of 4 μm. A vertical alignment film 14 having a thickness of 500 mm was formed on the stripe electrode.

(1-2) Preparation of Second Substrate 20 An 800 mm thick ITO (indium tin oxide) film was formed on the entire surface of a plate glass (upper substrate 21) having a thickness of 0.7 mm to form the counter electrode 22. Subsequently, an acrylic resin having a thickness of 3 μm was formed as an insulating film 23. A vertical alignment film 24 having a thickness of 500 mm was formed on the insulating film 23.

(1-3) Preparation of the liquid crystal layer 30 ε // (relative permittivity in the major axis direction) is 24.7 and ε⊥ (relative permittivity in the direction perpendicular to the major axis direction) is 4.3. A liquid crystal material in which 0.6% by mass of a polyfunctional monomer having a liquid crystal skeleton was added to a liquid crystal having dielectric anisotropy was used. Furthermore, 6 mass% of shape anisotropic particles 32 obtained by resin coating on aluminum (Al) flakes were added. The relative dielectric constant of the shape anisotropic particles 32 was about 3.5. The diameter (maximum length) and thickness of the shape anisotropic particles 32 were about 6 μm and 0.1 μm, respectively. The thickness of the liquid crystal layer (cell thickness) was 10 μm.

(1-4) A rectangular wave 20Vp-p (a voltage waveform of ± 10V after being set to + 20V and 0V) is applied to the stripe electrodes (the pair of

electrodes

12a and 12b) of the PSA-treated first substrate 10, and the second With the counter electrode 22 of the substrate 20 at 0 V (GND), ultraviolet irradiation was performed from the second substrate 20 side, the PSA monomer 33 was polymerized, and

PSA films

15 and 25 were formed.

(1-5) Attaching the light absorber Finally, a black acrylic plate as the light absorber 16 was optically bonded to the back side of the lower substrate 11. Here, the optical adhesion means that a substance having an appropriate refractive index is interposed in order to prevent an air layer from being formed between the lower substrate 11 and the light absorber 16. In the example, glycerin was used as the substance having the appropriate refractive index. When the light absorber 16 is disposed under the lower substrate 11 without optically bonding, an air layer is formed between the lower substrate 11 and the light absorber 16, and thus strong interface reflection occurs. As a result, the black transmittance may increase (that is, the contrast will decrease), or the double image (blurring) of the display may occur.

(Characteristic evaluation)
Below, the evaluation result of the reflection type display apparatus produced with the method of Example 1 is demonstrated. However, for comparison, the reflective display device used in the characteristic evaluation is the one in which only the right half of the display area is subjected to the PSA process as in the first embodiment and the left half is not subjected to the PSA process.

(2-1) Evaluation of Brightness in White Display State The white display state of the reflective display device was photographed. FIG. 6 is a photograph comparing the white display state of an area where the PSA process has been performed (right side of the figure) and an area where the PSA process has not been performed (left side of the figure). The applied voltage for white display was 10 Vp-p in both regions. As shown in FIG. 6, the area where the PSA process has been performed (right side in the figure) is whiter than the area where the PSA process has not been performed (left side in the figure), and the brightness of white has been improved. I understand that

FIG. 7 is an enlarged microscopic photograph showing the area where the PSA process shown in FIG. 6 was not performed, and FIG. 8 is an enlarged view showing the area where the PSA process shown in FIG. 6 was performed. It is the microscope observation photograph. In FIGS. 7 and 8, flake material that contributes to white display appears white, and flake material that does not contribute to white display appears black. In FIG. 8, the area that appears white compared to FIG. 7 is clearly wider, and the flakes that contribute to white display increase in the area where the PSA process is performed than in the area where the PSA process is not performed. I understand.

(2-2) Evaluation of reflectance-voltage characteristics (RV characteristics) The reflectance-voltage characteristics of the reflective display device were measured, and the obtained results were graphed. FIG. 9 is a graph showing the reflectivity-voltage characteristics (RV characteristics) of the PSA untreated area and the PSA treated area. In this measurement, the applied voltage was gradually increased from 0 Vp-p to 20 Vp-p and then gradually decreased to 0 Vp-p. An integrating sphere was used as the light source, and the reflectance of the standard white plate was 100%.

From the result shown in FIG. 9, it can be seen that the white reflectance is improved in the PSA processing area. For example, at a voltage of 10 Vp-p when the applied voltage was increased, the reflectance of the PSA untreated area was 13% and the reflectance of the PSA treated area was 27%, and the reflectance increased approximately twice by the PSA treatment.

Furthermore, it can be seen from FIG. 9 that the improvement (area reduction) of the hysteresis loop of the RV curve (deviation of the RV between when the applied voltage is increased and when it is decreased) is achieved by the PSA process. For the measurement results of the PSA treated area and the PSA untreated area, when the applied voltage is increased, the reflectance at 0 Vp-p is normalized to 0, and the reflectance at 20 Vp-p is normalized to 1, and the area of the hysteresis loop is obtained. Furthermore, when the area of the PSA unprocessed area is 1, the area of the PSA unprocessed area is 0.4. That is, an improvement of 60% was observed. Improvement of the hysteresis loop is important for easily realizing gradation display.

[Appendix]
Examples of preferred embodiments of the light modulation device according to the present invention will be given below. Each example may be appropriately combined without departing from the scope of the present invention.

The polymer layer is preferably formed by polymerizing a monomer having a liquid crystal skeleton added to the liquid crystal. A monomer having a liquid crystal skeleton is easily mixed in the liquid crystal, and thus is easily distributed uniformly in the liquid crystal. For this reason, a polymer layer can be uniformly formed with a small addition amount. In addition, the liquid crystal skeleton taken into the polymer layer can exert an alignment regulating force on the liquid crystal molecules. Since this liquid crystal skeleton is rigid, it is not easily bent by the movement of liquid crystal molecules, and a pretilt angle can be stably imparted. Thus, by using a monomer having a liquid crystal skeleton, the orientation of liquid crystal molecules can be effectively controlled, and a uniform pretilt angle can be imparted.

The shape anisotropic particles are preferably those in which a metal flake is coated with a resin. By using such shape anisotropic particles, the difference in dielectric constant between the liquid crystal and shape anisotropic particles can be increased, and good switching characteristics can be obtained.

The pair of electrodes may constitute an IPS type electrode structure, or may constitute an FFS type electrode structure. When configuring an IPS-type electrode structure, the pair of electrodes is a pair of comb-teeth electrodes with which the comb teeth are fitted. When configuring an FFS-type electrode structure, the pair of electrodes is a combination of a planar electrode and an electrode in which an electrode slit is formed. In either the IPS type electrode structure or the FFS type electrode structure, a transverse electric field can be formed in the light modulation layer, and the liquid crystal and shape anisotropic particles can be aligned in the horizontal direction. Further, according to the IPS-type electrode structure, the number of layers constituting the first substrate and / or the second substrate can be reduced, so that the number of steps required for film formation and patterning of the layers can be reduced. On the other hand, according to the FFS-type electrode structure, the possibility of a short circuit between the electrodes can be reduced, and the influence of static electricity from the outside of the light modulation device can be prevented by the planar electrode.

The second substrate preferably has a planar electrode facing the pair of electrodes. By providing a planar electrode on the second substrate, a vertical electric field can be applied to the light modulation layer. The light modulation device of the present invention can be operated only by a horizontal electric field, but a vertical electric field may be applied as necessary. For example, the application of a longitudinal electric field is effective for the purpose of resetting hysteresis, resetting the alignment disorder of shape anisotropic particles due to impact from the outside, electric field assist for high-speed response, and the like.

Below, the example of the preferable aspect of the display apparatus which concerns on this invention is given. Each example may be appropriately combined without departing from the scope of the present invention.

The display device preferably includes a plurality of pixels arranged in a matrix, and the first substrate preferably includes the pair of electrodes on each of the plurality of pixels. With such a configuration, high-definition display is possible.

The display device preferably performs display by reflecting external light with the shape anisotropic particles in the lateral electric field state. With such a configuration, display in a reflection mode or a semi-transmission mode (a combination of a transmission mode and a reflection mode) is possible.

It is preferable that the board | substrate located in the back side among said 1st board | substrate and said 2nd board | substrate has a light absorption layer. By providing the light absorption layer on the substrate on the back side, the contrast ratio can be increased in reflection mode display.

10: First substrate 11: Lower substrate
12a, 12b: electrodes 14, 24: vertical alignment film 15, 25: PSA film 16: light absorber 20: second substrate 21: upper substrate 22: counter electrode 23: insulating film 30: liquid crystal layer 31: liquid crystal molecule 32: Shape anisotropic particle 33: PSA monomer 40: light source 112a: first electrode 112b: second electrode 113: dielectric layer

Claims

A first substrate and a second substrate disposed opposite to each other;
A light modulation device comprising a light modulation layer disposed between the first substrate and the second substrate,
The first substrate has a pair of electrodes,
The light modulation layer is obtained by dispersing shape anisotropic particles in liquid crystal,
The liquid crystal and the shape anisotropic particles are aligned in a direction perpendicular to the first substrate in a state where no voltage is applied between the pair of electrodes, and a voltage is applied between the pair of electrodes. In an electric field state, it is inclined in a horizontal direction with respect to the first substrate,
A light modulation device, wherein a polymer layer having a surface shape that supports the inclination of the shape anisotropic particles in the transverse electric field state is provided on a surface of the first substrate on the light modulation layer side.
The light modulation device according to claim 1, wherein the polymer layer is formed by polymerizing a monomer having a liquid crystal skeleton added to the liquid crystal.
3. The light modulation device according to claim 1, wherein the shape anisotropic particles are obtained by coating a thin metal piece with a resin.
The light modulation device according to any one of claims 1 to 3, wherein the pair of electrodes is a pair of comb-teeth electrodes in which mutual comb teeth are fitted.
4. The light modulation device according to claim 1, wherein the pair of electrodes is a combination of a planar electrode and an electrode in which an electrode slit is formed.
6. The light modulation device according to claim 1, wherein the second substrate has a planar electrode facing the pair of electrodes.
A display device comprising the light modulation device according to any one of claims 1 to 6.
Having a plurality of pixels arranged in a matrix,
The display device according to claim 7, wherein the first substrate has the pair of electrodes in each of the plurality of pixels.
The display device according to claim 7, wherein the display device performs display by reflecting external light by the shape anisotropic particles in the lateral electric field state.
The display device according to claim 9, wherein a substrate located on a back side of the first substrate and the second substrate has a light absorption layer.